Our transcription: The collisions that we've just seen may seem completely unrelated to this serene and beautiful landscape, but, in fact, this valley and these mountains are the direct result of very similar types of interactions between two of the Earth's adjacent plates. Plates are the rigid slabs of rock that comprise the outer surface of the Earth. They're tremendous in size, sometimes encompassing entire continents, and they're moving and interacting with one another at their boundaries. Because the plates are rigid, their interiors are relatively inactive tectonically. The boundary between plates, however, is defined by a high degree of tectonic activity. Plate boundaries coincide with narrow zones of earthquakes, and active volcanoes, rapidly rising mountain ranges, and deep sea trenches. This long linear valley is one such plate boundary. This is the San Andreas Fault in California. On this side, the North American plate is grinding fitfully against the Pacific plate over here. The result of this interaction are sudden and sometimes devastating earthquakes. Over time, this interaction has resulted in the steady uplift of these mountain ranges. Plate boundaries are directly related to geologic hazards, to the formation of petroleum and mineral resources, and to the geologic development of the landscapes on which we live. So understanding how plates move and interact at their boundaries is not only one of the most interesting, but also one of the most important goals of the current generation of Earth scientists.